On Dec 10, 2004, at 9:03 PM, Robert Dorchuck W6VY wrote:
I am trying to rebuild a SB-220 amp. I found what appears to be a
resistor in place
of the RF choke on the grid of both tubes (RFC-4 and 5, 1 mh
pi-wound). The color
coding is yellow-violet-black-red and it measures 47 ohms which almost
matches the
color code.
Can anyone point me to a source for the correct choke or suggest a
good replacement.
Any help appreciated.
Bob -- The 47-ohm resistor acts as a grid-fuse / I-limiter. During a
110MHz parasitic oscillation or a sudden antenna disconnect, this
resistor burns out and protects the tube from a (fatal) grid-filament
short. My free, unsolicited advice is to locate a free supply of
3-500Zs Before you remove the resistor and go back to an RFC. ///
Does the 220 have carbon-comp parasitic-suppressor resistors with the
coils wound on top of the resistors? tnx
Thanks.
Bob W6VY
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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